1. Field of the Invention
The present invention relates to a semiconductor package structure. More particularly, the present invention relates to a semiconductor package structure with a protection bar that can prevent package warpage.
2. Description of the Prior Art
There are continuing efforts to improve the reliability of the plastic package technology for encapsulating semiconductor devices. A main cause for the lack of reliability in the plastic packages has been that materials having different physical characteristics are in contact with each other. For example, differences in coefficient of thermal expansion among a molding compound which forms the package body, a semiconductor chip which is made of silicon, and solder balls consisting of tin alloy, can cause separation of the materials during subsequent reliability testing. The aforesaid reliability testing is typically used to assess thermal stress and strain concentration on the solder joints between the chip and the chip carrier, which may cause potential fatigue failure of the system.
FIG. 1 is a schematic degree-of-warpage vs. temperature graph during a thermal cycle implemented in a conventional reliability testing process for a chip package. As shown in FIG. 1, the mismatch of the coefficient of thermal expansion between the chip carrier and the molding compound leads to different warping effects on the package during the thermal cycle. After cooling to a relatively low-temperature zone, the package bows and the side view of the package is analogous to a convex curve (crying curve). The contraction difference produces compressive stress on the solder joints. In a relatively high-temperature zone, the package warps and the side view of the package is analogous to a smiling curve. Therefore, in a relatively high-temperature zone, the solder joints are subjected to tensile stress. When the solder joints are twitched due to compressive stress and tensile stress repeatedly concentrated thereto, the solder joints may not tightly bonded to the bond pads on a printed circuit board (PCB), causing failure of electrical connection between the package and the PCB.
In light of the above, there is a strong need in this industry to provide an effective solution to solve the aforesaid package warping occurred during the thermal cycle implemented in a reliability testing process for a chip package, thereby effectively avoiding damage to the electrical connection between the package and the PCB and improving reliability.